Introduction

Beginning in 1993, researchers from the Andrews Experimental Forest Long-Term Ecological Research (LTER) have been monitoring populations of Pacific Giant Salamanders, Dicamptodon tenebrosus, specifically in Mack Creek (Gregory 2016). The Experimental Forest is part of the Willamette National Forest in western Oregon and managed by the U.S. Forest Service and Oregon State University (Figure 2.). Researchers are interested in how disturbances in forests effect biota. The data was collected from two sections of of Mack Creek - a clear cut section and an old-growth section. Here, we will use the data collected by the Andrews Experimental Forest Team to compare the differences in size and weight distributions of salamanders from clear cut and old growth sections.

Figure 1. A Pacific Giant Salamander (Dicamptodon tenebrosus) laying on a down log. Photo credit: Gary Nafis, www.californiaherps.com.

Figure 2. Map of HJ Andrews Experimental Forest LTER in Oregon. Andrews Experimental Forest is managed by the U.S. Forest Service and Oregon State University.

Data and Methods

Anne-Marie

Results

Results A: Annual salamander counts in old growth and clear cut sections of Mack Creek

Salamander counts in old growth and clear cut sections were compared between 1993 and 2017. Overall, salamander counts in both sections followed similar patterns; when counts in old growth sections were high (>200), counts in clear cut sections were also high. In 1994, 2011, and 2015-2017, salamander counts were higher in clear cut sections than old growth sections. In total, old growth sections had higher populations of salamanders (n = 5,951) compared to clear cut sections (n = 5,051) over the 17 year period.

Figure 3. Salamander counts in clear cut (orange) and old growth (green) sections of Mack Creek. Old growth sections are responsible for higher counts of salamanders for 80% of the time between 1993 and 2017. The populations in both sections display similar patterns of highs and lows. Data: Stanley Gregory, Andrews Forest LTER Sites.

Results B: Table of 2017 salamander counts by channel classification (pool, cascades and side-channel) in old growth and clear cut sections of Mack Creek.

Channel Type Clear Cut Forest Old-Growth Forest
Cascade 247 (55.1%) 201 (44.9%)
Pool 31 (40.8%) 45 (59.2%)
Side Channel 90 (54.9%) 74 (45.1%)

not sure why getting that error message. its not affecting the table counts/proportions (ex/when change position from front to rear dont get the error message)

Results C: Chi-Square test to determine if there is a significant difference in where in the channel Pacific giant salamanders are located (pool, cascade or side channel) between the two old growth and clear cut forests.

i cannot get rid of the unittype/channel type column for the chi squared subdata!!

Results D: Is there a significant difference in mean weights for Pacific giant salamanders observed in clear cut vs old growth forests in 2017

## 
##  Welch Two Sample t-test
## 
## data:  weight by section
## t = 1.6669, df = 692.79, p-value = 0.09599
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -0.2121307  2.5972032
## sample estimates:
## mean in group CC mean in group OG 
##         7.775870         6.583333

double check wording of the data spread conclusion to labs we’ve done with allison

Results E: Is there a significant difference between mean Pacific giant salamander weights in the 3 channel types: pools, cascades and side-channels of Mack Creek in 2017?

##               Df Sum Sq Mean Sq F value Pr(>F)  
## channel_type   2    757   378.4   4.216 0.0151 *
## Residuals    684  61403    89.8                 
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 1 observation deleted due to missingness

Summary

References

Gregory S. V. 2016. Aquatic Vertebrate Population Study in Mack Creek, Andrews Experimental Forest, 1987 to present. Environmental Data Initiative. https://doi.org/10.6073/pasta/5de64af9c11579266ef20da2ff32f702. Dataset accessed 11/25/2019.